“This is a ticking time bomb. We would encourage people to come to us. It's very important people think about their money in the short and the long term,” Hugh Stickland from Citizens Advice told the BBC.

“We think the banks could be doing more here,” he added.

Far fewer banks offer interest-only mortgages than in the 1980s and 1990s. But the problems are expected to start in 2017 when endowment mortgages sold in the 1990s reach their peak period of maturing.

Banks and building societies have been told by regulators to write to their customers to warn them that they could be in financial danger, according to the BBC.